Contingency Plan
by Taliax
Summary: Vanitas did say that Aqua would make a good backup... He didn't think through all the issues that would come from merging with the strong-willed girl. Starts during the finale of Birth by Sleep. (Cover art by @ghostpajamas on tumblr)
1. Prologue

**A/N: Guess who's foolishly starting another multichapter :D So this is the Vanitas-and-Aqua-merge story I've been wanting to tackle for a long time. (Sorry, Unplanner, "SAGS" didn't make the cut for the final title xD) I kept putting it off because I had higher priority stories (...which I still do), but finally I just decided I had to write it anyway. I'm not abandoning "Stroke of Midnight," and I'm still working on the CaS-prizefic too, but I had to get at least some of this out of my system first.**

 **This will probably end up being a strange mix of dark and awkward, just considering the possibilities of Vanitas and Aqua sharing the same body. *sweatdrop* So yeah, just a warning ahead of time.**

 **This starts off right in the middle of BbS's finale at the Keyblade Graveyard.**

"Go take what Ventus owes you. And take Aqua's life."

 _Finally._ Vanitas nodded sharply before running towards the edge of the cliff. Terra pursued, but Vanitas didn't worry about that - the loser was too slow, even if Master Xehanort hadn't been around to keep him occupied. He grinned beneath his mask as he dove from the cliff, feeling the wind rush around him.

Wind. _Ventus._ His old name. Soon to belong to him again.

His grin only widened when he realized who was in the path of his fall. Really, they were making this too easy for him. He flipped in midair, readying his blade to strike down on the girl's unprotected skull -

" _Aqua!"_ Ventus shouted from the ground, and she looked up with a gasp. Just in time to see her destruction descending from above.

Or, just in time to stop it. He grit his teeth as her blade intercepted his, metal screeching at the contact. His feet crashed to the ground seconds later, sending a shock up through his knees.

" _You!"_ Aqua spat at him. Her eyes were just as fiery as the last two times they'd fought. It would be a pleasure to get to extinguish that flame once and for all.

"Missed me?" He smirked, not that she would be able to see. She shoved her keyblade against his, and he jumped back. Though irritated that he would have to wait more long seconds to merge with his other half, part of him was glad that she had intercepted his blow. After their previous encounters, it would it would be a shame to pass up one last thrilling battle. Adrenaline flooded his blood as he took up his taunting stance.

"How are you still alive?" She shouted even as she was already shooting blasts of Firaga towards him, not taking any chances this time. He snorted and cartwheeled out of the way.

"You really thought you finished me in Neverland?" He teleported behind her, then brought his keyblade down in an overhead blow. She twisted at the last second and took it on her armored forearm, which dented at the impact. "That was just the warm-up round."

"Aqua!" Ventus called from behind her. Vanitas rolled his eyes; his pathetic other half was still frozen solid. _Thanks, Xehanort. Freeze the idiot and drop him off a cliff; that's a_ great _way to protect your precious X-Blade._ If Aqua hadn't caught him, he would have had to go with his riskier backup plan.

"Shut up. You can't do anything for her," he said, springing back to avoid Aqua's barrage of strikes. She'd gotten faster since their last fight, he noticed. Braig hadn't done a very good job of wearing her out.

"Stay down, Ven!" She called back to him. "Let me handle this!"

Vanitas chuckled and aimed a ball of dark fire at her, but she dodged and retaliated with magic of her own. Her quick Thundaga jolted through him; he bit back a scream. Xehanort had done worse to him before. He could handle this.

He recovered quickly and sprinted forward just as she started glowing with her Thunderbolt command style. _Would it have killed you to teach me how to do that, Xehanort?_ Her sparking blade arced towards him; when he blocked it, the electricity ran down his weapon and numbed his arm, but he kept his grip.

 _Alright, playtime's over._

"Suffer!" He cried, leaping and crashing down on her from above. He struck twice, but on his third attack she called up a barrier barrier that absorbed the hit, then exploded outward. The shards sliced through his suit, leaving new trails of red. He shouted and reknit the dark fibers as he lunged forward again.

"Heal!" A warm green glow surrounded her, and he cursed. Yet another skill Xehanort had failed to teach his apprentice. He tried to take advantage of her vulnerable moment, teleporting to strike from behind.

"Too sl-" He bit off the taunt when Aqua struck his keyblade arm with the shaft of her blade.

And then time stopped. Or at least, that was how it seemed. He couldn't move; he couldn't breathe. Panic rose in his chest, but he couldn't even release it as an Unversed. It was just trapped there inside him, the way he was trapped in his own body, unable to escape, forced to watch as Aqua rained blow after blow upon him, teleporting and leaving afterimages in her wake.

 _She - when did she learn how to do that!?_ He barely thought before time resumed, and the pain of each attack hit him all at once. His mind hadn't been prepared; he doubled over, nearly dropping Void Gear.

" _Too slow,"_ Aqua mocked back as a new aura of energy surrounded her - one he didn't recognize. Not that he could think clearly through the pain his body was still trying to process. Was he seeing double? Had she hit his head that hard even through his helmet?

No - there _were_ two of her. More than two. With each move she made, a ghostly afterimage remained, like reality couldn't catch up to her. It looked almost like Vanitas's own attack, where he would leave an illusion decoy and strike from behind.

 _She… did she learn that from me?_ He wondered as he cartwheeled away, dodging her rapid attacks. There were so many illusions, it was hard to tell if he was avoiding the real one or not.

"Wow, Aqua!" Ventus cheered from the sidelines, still half-frozen. "You've got him now!"

Unfortunately, Aqua _was_ beating him, for now at least. And he would still have to fight his other half after this. If only he had the X-Blade already! But he couldn't forge with Ventus yet, not when the idiot was little more than a popsicle, incapable of fighting back.

He tried to take the offensive, which was nearly impossible with so many phantom Aquas crowding the battlefield. He sliced through a few only for them to flicker like static and disappear. Then he finally targeted the real one, mostly because she brought the fight to him. Their blades clashed with sharp, piercing clangs.

They danced back and forth, blurs of blue and black, trading blows, parrying strikes, shooting magic. For a while and in spite of her illusions, Vanitas actually managed to gain the upper hand. There was a pattern to the phantoms, and once he saw it, it was easy enough to find the real one. And for whatever reason, she didn't come cleanly out of her cartwheels in this command style. Maybe she was still learning how to use it.

Just as she was looking ragged enough for him to end the fight, she unleashed her finish command. She leapt into the air and dove down over and over again, creating a star of magic that exploded with light at the end. Vanitas executed a sloppy cartwheel, just effective enough to dodge the worst of it. The light still burned his skin through his suit.

She came out of her finish breathing hard - but then again, so was he.

"Give it up already," she shouted, though her voice was hoarse from the dry air. "I'll never let you hurt Ven!"

Exhausted as she must be, her eyes still burned as fiercely as at the start of their battle. Maybe even more. And suddenly, he knew she was right. As desperate as he was to be whole, to unite with his other half, he would never be able to do it with Aqua still standing. Because somehow, against all reason, she was just as desperate has he was.

"Why do you care so much about that loser?" He asked, with equal parts spite and curiosity. "All he's done is use you. Hurt you. If it weren't for him, none of you would be in this mess."

"Aqua…" Ventus murmured from behind her, his face falling. "I'm sorry-"

"No." Aqua's eyes narrowed at Vanitas, though her words were aimed towards her friend. "I wish you would have listened to me, but this _freak_ would have come for you regardless."

Vanitas ground his teeth against the insult. Somehow, of all the things she'd said and done, that barb dug the deepest. Probably because it was true.

 _But not for long. As soon as I merge with Ventus-_

Which he couldn't do. Not until he defeated Aqua. And just like in Neverland, they were at a stalemate - only this time, he couldn't risk exerting all his energy on this fight.

 _Unless… I decide to take a different risk._ Unversed of fear squirmed inside him as he thought of his backup plan. That plan could very well get him killed - but then again, if her and Ventus were too unbalanced, he could die from that union too.

The risk would be worth it. He had to forge the X-Blade - he _had_ to. There was no other choice.

He threw himself back at her, ignoring the fatigue that threatened to drag him down. He had to give this fight everything he had - and he had to make sure she did, too.

"You really think you can save him?" He taunted as their blades locked again. His mask was only inches from her face. "There's only one way to stop me from killing him."

Her face hardened, her lips drawing to a thin line. "Whatever it takes, I'm willing to do it."

She cast Seeker Mine, sending pools of magic to home in on his feet and blow him back. He backflipped out of the explosion and landed on his feet, skidding back and throwing up dust.

"I hope you mean that," he said through a smirk. Then he slid forward in a powerful but reckless combo, his blade streaking so fast it nearly left afterimages without the aid of magic. She parried and dodged, and her armor absorbed the few hits she couldn't block.

 _I could use some armor like that._ Well, if this worked, he might have it shortly.

Sweat dripped down her face, but she didn't give up. Good. Vanitas wasn't expecting her to. But she was still on the defensive; he needed to taunt her into retaliating again.

"Come on, _Aqua._ I thought you were the Keyblade Master here." His words produced a spark of anger in her eyes, but she quickly reverted to calm. That was the problem - in spite of the danger, she was still disciplined, still in control. Not as easy to unravel as her friends. But there _was_ one thread he knew he could tug on.

He teleported behind her, but this time, he didn't go in for the attack. Instead he stood behind Ventus, raising his keyblade high over his chest.

" _Aqua!"_ The other boy shouted, panic flashing over his half-frozen face. It was uncanny, seeing his old face stare up at him like that, practically begging for mercy.

"Pathetic," he spat as he quashed the conflicted Unversed inside him. "You always need your stupid friends to come save you. When are you gonna grow up?"

He didn't hear Ventus's reply - because at that moment, a giant crystal of ice burst from the ground, launching him into the air. He crashed to the ground a few paces away, gasping for breath. Then Aqua's metal boot was planted in his chest.

"You - will _not - hurt him!"_ She snarled down into his face. His muscles tensed unconsciously, but he forced himself to keep his voice even.

"Then you're going to have to kill me, _Master_ Aqua."

Her face stayed as hard as steel. "That can be arranged."

Vanitas's eyes widened. That was exactly what he'd wanted - for her not to hold back. But that look on her face… if she could look at him with that much hate, did she really have enough light to forge the X-Blade with him?

His mind hesitated, but her keyblade didn't. The tip of the cobalt weapon released a blast of brilliant white light.

Vanitas screamed. Every nerve erupted in pain. His heart released all the Unversed he'd been holding back throughout the fight, but as soon as they were born, they dissolved in the face of the scorching light.

And then, he began to dissolve with them.

 _Maybe… she does have enough light…_

His last thought was to hope so. Otherwise, he'd just made the most foolish mistake of his life.


	2. X-Blade

**A/N: Sorry for the long wait on this! I've been in over my head with classes this summer, but things should be easing up now. I've still got a few finals left but I got the worst one over with. Anyway, this chapter isn't very long, but I hope you enjoy!**

 _Huh… is this what dying feels like?_ Vanitas wondered as he drifted in the light. _Never thought it would be so… warm…_

Then his feet touched down on something solid. So he wasn't dead, probably. Which could only mean...

"It worked," he whispered to himself as his eyes opened. He was standing on a glass platform, as Xehanort had said might happen. Though, if Xehanort's theory had been correct, Vanitas's image would have been the only one on the glass. Instead, another figure mirrored his.

" _Aqua_ ," he scoffed. As if her name had summoned her, she floated down on the opposite side of the platform from him. For some reason her protective armor had disappeared, leaving her in her usual impractical-looking outfit. Her gaze darted frantically around the surrounding emptiness before locking on him.

"Vanitas! But this is - what are you doing in my heart!?"

So she knew this place too. That was to be expected - all keyblade wielders had their Awakenings in places like this, even if he didn't remember his own personally. Those memories were still trapped within Ventus. He regretted that he would probably never get them back now that he'd chosen Aqua, but it was too late to worry about that now. His mind was occupied with only one question.

"Where's the X-Blade?" He demanded, summoning Void Gear. Aqua stared at him like he was an idiot, but summoned her own weapon.

"You mean the one you're holding?"

"No, not - ugh, it's a _Kye-_ Blade, not a _key_ blade, you idiot. Our union should have forged-"

"You mean you knew this would happen?" Aqua interrupted. "You - tell me what you've done to me!"

Vanitas was in no mood to answer questions, especially not to a girl who'd tried to kill him. He darted around the edge of the platform, staring down into the void below. Could the X-Blade have fallen down there somehow? There was no way to know what should have happened; all the ancient records of the X-Blade were vague at best and completely useless at worst. Xehanort had just promised that it would _work._

Aqua took his sudden movement as an invitation to attack again. He was so focused on looking for the X-Blade that he didn't notice until he heard the fireballs rushing towards him. He cursed and cartwheeled away, but one still singed his leg.

"Agh…!" Aqua cried, falling to one knee. Vanitas regained his footing, shook off the pain, and raised an eyebrow under his mask.

"If this is some kind of fake-out move, I'm not falling for it."

But Aqua just shouted a battle cry and started shooting magic again. This time Vanitas was ready for it, but the rage she'd shown before hadn't subsided. Her reckless spellcasting was impossible to evade completely, especially when he so close to the edge of the platform. He took a Blizzaga in the chest and stumbled back. As his boot brushed the edge of the glass, Aqua screamed again.

"Why… why does it hurt…?"

Vanitas didn't know, but he wasn't above taking advantage of it. He rushed forward and swung Void Gear at her unprotected waist -

 _Light warmth burning Love protect fight -_

"Agh-!" He staggered back from what felt like a physical explosion of light, but when he blinked his eyes open, Aqua was on her knees from his blow. "What the - what did you do!?"

She looked up through her disheveled bangs to give him her signature glare. He was going to regret this whole backup plan if he had to spend the rest of his life trapped with that.

"That's what I asked you, _idiot,"_ she mocked him. He snarled and went in for another attack. She parried a few blows before one slipped through -

 _Determination strength light hope Love win -_

He recoiled again, hissing this time. Those feelings flashing through him… Xehanort hadn't warned him of this, but he began to form a theory. If he was right, he may have just made his heart into a prison. He needed the X-Blade now more than ever.

With one last snort of derision towards Aqua, he turned away and went back to searching the darkness below.

"You really think you're going to find this X-Blade?" She called as she got to her feet.

"I have to," he said to himself. "Xehanort, if you lied to me, I swear I'll kill you…"

"Huh?" Aqua let out a small noise of surprise. Vanitas snorted again but didn't turn to face her.

"What, surprised I'm not loyal to that old geezer? He can rot in the Realm of Darkness for all I care, as long as I-"

Aqua gasped. The timing was strange enough that Vanitas looked over his shoulder -

Only to see the very weapon he'd given his whole existence to forge in the hands of his opponent.

He paused for a moment, awestruck. He had never seen a complete picture of the X-Blade, but he instantly knew that this was it. Two Kingdom Keys crossed at their shafts, with dark webbing filling the gaps between them. From its top protruded a shadowy but sharp blade. But there was something about it… the way it pulsed eccentrically, its chipped edges, one of the missing handguards. It was broken.

 _No, not broken. Just not yet finished._

"Ven… Ventus?" Aqua whispered, her eyes wide as she gripped the X-Blade by one of its two black handles.

" _No!"_ Vanitas snapped out of it and sprinted towards her, boots pounding against the hard glass. Seemingly enthralled by her new weapon - _his_ new weapon - Aqua didn't even flinch. In fact, she didn't seem to acknowledge his presence at all. That was probably for the best, as she would be much more powerful than him with the X-Blade in her grasp.

 _But not for long,_ Vanitas thought as he dove for the opposite handle of the blade. His fingers closed around it, and -

" _Aqua? Aqua!" Ventus rushed towards him, kicking up clouds of dust. Shards of ice still fell from his armor. "What happened? Did you beat Vanitas?"_

" _What?" Vanitas said, but his voice was all wrong. Too high. And why did Ventus look so short? "I_ am _Vanitas, you idiot."_

Suddenly the X-Blade was jerked from his grip, and the vision of the Keyblade Graveyard disappeared. He shook his head, disoriented by the sudden shift.

"You - _freak!"_ Aqua was shouting at him. His vision was still a little blurry, but he could easily make out Stormfall pointed at his throat. Where had the X-Blade gone? What was _happening?_

"How did you do that!?" She demanded.

"Do what?" He snapped back, rubbing the side of his helmet, not that it did much for his head underneath. Maybe it would be worth it to take the stupid thing off. After all, if Aqua was paying any attention, she could see his unmasked face on the platform below.

"Don't act like you don't know!"

"I _don't_ know!" He threw his hands in the air, finally abandoning the last of his frayed composure. "None of this was supposed to happen! The X-Blade should've been _mine-!"_

That was when he saw it. Floating behind her, as if oblivious to how badly he wanted it, needed it. Why had Aqua let go of the ultimate weapon?

That didn't matter; if she was going to be that stupid, he wasn't going to stop her. He slipped around Stormfall and lunged for the X-Blade - only to have her cast a Barrier spell around it. His hand bounced off uselessly.

"You're not getting the X-Blade," Aqua said, her voice darkly calm this time. Somehow that was even scarier than when she had yelled at him all the times before. Still, he summoned Void Gear and took up his battle stance.

"You think you can stop me?"

"I saw what happened before," she replied, keeping Stormfall in a defensive position. "For whatever reason, you can't hurt me without feeling pain."

So she'd noticed. "And you can't hurt me, either," he retorted.

"Perhaps not. But I can keep that weapon out of your hands."

"You - you…" _You can't,_ he wanted to say. But… with a spell like her Barrier… _Think, Vanitas!_ His eyes flashed to the X-Blade, hovering just inches out of his reach, taunting him.

 _You really thought you could be whole?_ It seemed to say. _Get real. You were a loser before, and you're an even bigger loser now. You'll never be anything but an abomination._

"Nngh… shut up!" He shouted, channeling his anger, his hopelessness, into an Unversed. Or at least, he tried to. Despite his strong emotions, none of the creatures stirred beneath his skin. "What… why aren't you…"

"If you're done throwing your temper tantrum, you should get us out of here," Aqua said. Vanitas laughed, a cackle that started low and slowly rose in pitch.

"You want to finish joining with me, then? That's the only way I know to get out."

" _Join_ with you?" Aqua grimaced in disgust. "What do you mean?"

Vanitas rolled his eyes, but decided to answer the question this time. After all, if he could distract her long enough, maybe he could find a way to get the X-Blade.

"Just look around. This place should tell you everything you want to know." He gestured to the glass floor. "By destroying my body, you freed my heart to join with yours. A union of two hearts - one light, one dark. That was all it took to forge the X-Blade."

Aqua stared at the weapon as horror slowly dawned on her. That expression almost made this whole mess worth it.

"You… you used _me,_ instead of Ven. That was your plan all along, wasn't it?"

"Don't think so highly of yourself," he snorted. "You were just the backup. Ventus wouldn't have given me half as much trouble."

"...I still don't understand. Why did you want Ven?"

Vanitas laughed. "So he didn't tell you, did he? Ventus is my other half."

He let that sink in for a moment. Rather than horror this time, though, her face only showed anger.

"Like Ven could ever be connected to someone like you!"

"Not just connected. Your precious Ventus _was_ me." He smirked under his mask. "If you had met him before we were separated, well…"

Aqua lifted her blade like she wanted to strike, then restrained herself. Vanitas wished she hadn't. If she could lose control long enough to hurt him - and in the process, hurt herself - he could have time to shatter her Barrier and steal the X-Blade.

"That's why he ended up with you, you know," he continued calmly. "Xehanort needed someone else to babysit the loser after he split us in two."

Her eyes flashed. " _Xehanort_ did that?"

"Don't tell me you're surprised. Hmm, I wonder what he'll do with Ventus now that he's useless…"

"I won't let him!" Aqua's eyes darted around frantically. "I have to stop him…!"

"Good luck with that." Vanitas snorted. "Even if you _can_ get out of here, there's no way you can beat Xehanort. Especially if he's already got Terra."

"He won't! Terra won't give in to the darkness!" Aqua placed her free hand over her heart. "And even if I'm stuck here… I know he can keep Ven safe."

He let out a sharp, surprised laugh. "You - you have no idea, do you? Xehanort doesn't just want your idiot friend to fall into the darkness. He wants to take his body for himself."

Of everything he'd said to break her composure, that seemed to pierce her the deepest. She took a step back, her keyblade arm going limp.

"Xehanort wants… _what?"_

"You heard me. The geezer's getting old; his body won't last forever. But if he could extract his heart and put it a younger vessel…"

"That's insane!"

Vanitas shrugged. "I've already put my heart inside you. You know it can happen."

She stood there, staring at the keyblade in her hand, then looked up in determination. That was all the warning he received before she rushed in for an attack. He brought up Void Gear, but the force of her blow still knocked him back. He chuckled and spread his feet in a more stable stance.

She cast Thundaga Shot; he sprung to the right, letting it zap the glass image of his knee. That and her time-warping spell were two he would need to avoid, but he still needed to take at least a small hit…

 _There._ She was summoning small pools of light that zoomed towards him. Seeker Mine. He teleported away from the first two, but purposely materialized in the path of the third. It exploded under his feet, searing his legs. But that pain was inconsequential compared to Aqua's reaction. She stumbled as she ran towards him, wincing in pain.

He didn't waste time on a snarky remark; he only had seconds at best to pull this off. He vanished, but he left behind an afterimage that Aqua lunged towards.

Then he came crashing down, keyblade bared, on the barrier around the X-Blade.

"What-? Vanitas!" Aqua yelled, and then the shattering of the spell drowned out anything else she might have said.

 _Finally, finally, FINALLY-_

He dropped Void Gear in his haste to grab the X-Blade. His fingers closed around it, and-

" _Aqua, please wake up… please, you have to, we have to go help Terra…"_

"Nngh-" Vanitas blocked out Ventus's voice, shook off the sensation that his other half was holding his free hand. Was this some kind of side-effect of forging the X-Blade? Whatever, he could keep the vision at bay if he focused; that was what mattered now.

Aqua was coming in for another attack. As if she could stop him now. He swung the X-Blade in a wide arc, feeling it hum with power as it prepared to unleash a wave of energy at her.

And then, suddenly, she was gone. Vanitas blinked and mouthed half a curse before she appeared directly in front of him. Despite his newfound power, he flinched - was she going to use that awful time spell again? Would it still work, even with the power of the X-Blade on his side?

But she didn't attack. Instead she grabbed the opposite handle of the X-Blade with her free hand.

And then, against his will, Vanitas was pulled into another vision.

 **A/N: Forgot to mention at the beginning, but whoa, E3 was crazy, wasn't it? I don't know if I'll write anything with Aquanort/Dark Aqua soon, just because I played with that in CaS and there are so many other things I need to write. (Like the CaS bonus fic, which has been giving me a lot of trouble for various reasons. And Stroke of Midnight, which I still really want to work on, but I know as soon as I start again I won't get around to working on anything else for a while.) But I will probably do some Aquanort/Vanitas art at some point soon~**


	3. Control

**A/N: Guess what story isn't dead lol**

"Ughh…" Vanitas felt like throwing up. All this back-and-forth, suddenly finding himself in one place, then another… But he was in the Keyblade Graveyard again. He felt the dirt under his back; he saw the clouds swirling around a giant heart-shaped moon in the sky. Was this actually a vision? Or – and this was more likely, now that he thought about it – had his fight inside Aqua's heart been a vision, and this was the real world? Maybe he had been knocked unconscious, and his mind had invented that battle out of his desperation to forge the X-Blade.

But then what was the thick handle that he felt in his grip?

"Aqua!" Ven leapt up, grinning that stupid, giant grin that made Vanitas want to take a keyblade to his face. "I was so worried… Aqua?"

He wanted to frown and tell the loser to get his eyes checked, but his mouth rebelliously pulled into a smile.

"Ven, I'm so glad you're safe," his voice said. Only, it _wasn't_ his voice. His eyes widened. He bolted upright, free hand reaching up to touch his lips. How had he–

"I'm glad you're safe, too. But… where did Vanitas go? Is he…"

 _He's right here, you idiot!_ But things were starting to fall into place. When they'd merged, he must have kept Aqua's appearance. All Ventus could see was his his friend.

That might work to his advantage.

His – her – their? – face curved into a frown. Aqua's doing.

"It's… complicated," she said through their mouth.

"He's gone," Vanitas added. Aqua widened their shared eyes.

"Ven – I'm not–" She began to say, before he cut in again.

"You were saying something about _Terra,_ right?"

Ventus's eyes flickered across their face. His brows furrowed slightly – he was seeing through Vanitas's act. Stupid; he hadn't been able to keep the disgust out of the way he said Terra's name. Aqua would never do that.

"Aqua… your – your eyes…"

Vanitas laughed, nearly scaring himself with the sound. That wasn't his usual taunting laugh – somehow it was even more disturbing coming from Aqua's vocal chords.

"So you've figured it out, have you?" He may have Aqua's body, but his darkness must have bled out through her eyes. _His_ eyes; he could see their golden glint reflected in the chest plate of Ventus's armor. The fact that some physical part of him had carried over to his new form was comforting.

"Figured out… Aqua, what are you…?" Ventus stepped back, shaking his head slowly in disbelief.

"Tch. You're even dumber than you look." He shoved off the ground with his – Aqua's – arms, springing to his feet. The X-Blade remained a dense weight in his right palm. He noticed that this version glowed more brightly; its form was complete, flooding him with power. It felt intoxicating, as if he could've just stood there and held it forever, drinking in the light that wafted off of it. With its power, he could finish off Ventus here and now. The other boy still stupidly thought _Aqua_ was his friend; he wouldn't see it coming –

"Ven! _Run!"_ His mouth betrayed him again – or rather, it obeyed its original owner. Ugh, Vanitas's head hurt; all this back-and-forth, gaining and losing control –

"Aqua! You're not–!"

Before Ventus could finish the thought, Vanitas rushed forward. He didn't have much time; he raised the X-Blade high over his shoulder –

Only to be stopped in his tracks as his own muscles froze mid-stride.

"You heard me! _Run!"_ Aqua yelled. _"_ Get away from here! I'm not–!"

"Nngh, _shut up!"_ He squeezed their eyes shut. A twisting feeling of vertigo overtook him. Then in the darkness, he could see it again – the pillar representing their merged heart. And more importantly, Aqua standing frozen beside him, clutching the other handle of the X-Blade.

"Stop fighting me!" He snarled at her.

"Get out of my heart!" She snapped back, trying to jerk the incomplete X-Blade from his grip.

"Where else am I supposed to go, _Master_ Aqua? In case you didn't notice, you _killed_ me!" His anger bled into his voice, giving away more of his true thoughts than he should have. If she noticed his desperation though, she didn't care.

"Apparently I didn't do a good enough job of it." Her blue eyes burned hot. He was in her heart, he _had the X-Blade,_ and he _still_ couldn't wipe that look off of her face!

"You can't hold me off forever," he shot back. "I'm a part of your heart now. _Permanently._ There's no way to destroy me without destroying yourself."

Her gaze hardened. Wrapped around the X-Blade, her fingers bleached white.

"I told you I would do whatever it takes. Anything to save Terra and Ven."

He searched her eyes, looking for any sign of weakness. He found none. If she had to destroy herself to put an end to him, she would really do it.

"I thought you might be smarter than those two idiots. Guess I was wrong." He shrugged. He was just stalling – she might be willing to destroy him, but the feeling wasn't mutual. He _wanted_ to stay alive, thank you very much. Even if that meant sharing a body with someone who wanted him dead.

"You really want to save Terra and Ven, huh?" He smirked, getting an idea. "You can't do that if you kill us both. I'm not the one they need to worry about now."

She looked away, her gaze focusing on the X-Blade.

"But they _should_ be worried. This blade… it could destroy both of them. It shouldn't exist. No one should have this kind of power."

So she could feel it too – the raw magical power coursing through the blade into them. Linking them together, whether they wanted or not. Through it, Vanitas could feel some of her light, her thoughts – and she was scared. Not of him, but of the weapon they held.

"Well it _does_ exist," he said. "And as much as I hate to admit it, _you_ have half of that power. Which means you help decide how we use it."

Her gaze locked back on him.

"What are you saying?" Her voice was laced with skepticism, as it should be. For once though, he was telling the truth. If she could feel anything from him in return, she would know that.

"I'm _saying–"_ he gritted his teeth, "I can't use the X-Blade without you. You tried it too; you know I'm right. We can't move our body without working together."

" _Our_ body – my body belongs to _me,_ you–!"

"Blah, blah, blah," Vanitas interrupted, rolling his eyes. "Look, I don't have time for your insults. I'm here whether you want me or not. So what are you going to do, Aqua? Are you going to stand here and fight me while Xehanort destroys your friends?"

She stared in stunned silence. "I… wait a minute. Are you saying you want to help me stop Xehanort?"

If she wanted to put it that way, sure. As long as it got her to stop fighting him.

"I don't know if you noticed, but he's the one who threw my original other half off a cliff. He didn't know you were my backup plan. That shows you how much he cares about me, and I can promise the feeling's mutual."

Aqua took a moment to process that.

"You were going to kill Ven. Or _merge_ with him – which is just as terrible, if you ask me."

"Which I didn't." He snorted. "He's useless to me now, though." As much as he'd still rather be rid of his other half, it was better to leave him alone, if it meant winning Aqua over.

" _That's_ comforting," she muttered. "But… I don't have much of a choice, do I? Terra's still fighting Xehanort…"

"And probably losing, if you don't stop talking and do something about it."

She looked away, but he didn't miss the expressions that flickered across her face. Fear, grief, determination. He felt the emotions through their connection as much as he saw them. She hadn't been worried for herself, but when it came to Terra and Ventus… they were his only bargaining chips. They'd stay safe for now, then.

"How do we get back to them?" She finally asked him.

"Probably the same way we did the first time. Close your eyes here while holding the X-Blade, and you should show up in the real world again."

"Alright. But you need to close your eyes with me. That was the only way we could work together."

She was right about that, but more importantly, she was probably trying to make sure he didn't steal the incomplete X-Blade while she was distracted. That would've been a stupid plan though, considering how well it had worked last time.

"Fine."

"On three," she said, and he rolled his eyes. "One, two–"

He closed his eyes.

"Aqua? _Aqua!"_ Ventus was screaming way too close to his ears.

"Void, can you shut up for two minutes?" Vanitas groaned. Ventus sprung back, keyblade held in his backwards grip.

"I know you're not Aqua. Let her go, Vanitas!"

He rolled their eyes. "Took you long enough. We don't have time for you, though." He looked up at the heart-shaped moon glowing through the clouds overhead. Kingdom Hearts. He'd dreamed of this moment for so long – dreamed of fighting the keyblade wielders who were supposed to flock to this place. Fun as that would be, he realized now that it was too short-sighted. He had the X-Blade; he could destroy them them all, but then what? He didn't need some weird moon. He just wanted to be –

 _Whole. I'm still not whole._ He'd forged the X-Blade, but he still didn't feel any different on the inside, not really. Some of Aqua's light leaked through the incomplete X-Blade into him, but the greater part was still separate. He had to find a way to make her let him in...

While he was absorbed in thought, Aqua took control of their body. With the extra speed and strength granted by the X-Blade, she dashed towards the pillar of earth. He didn't fight her. Xehanort and Terra were still up there – or one of them was, at least. He hoped Xehanort hadn't taken over Terra yet; Aqua would be much less willing to fight him if he had the face of her friend.

With their newfound energy, they leapt onto the side of the plateau and ran up the rugged surface. Gravity barely seemed to tug at them. He added in his own willpower to Aqua's, and their speed increased until they were flying faster than the wind.

 _So this is what we can do if we work together._ For now at least, they had a common goal. What would he do when that goal was finished? How could he keep her from destroying him?

He didn't have time to think about that; they were vaulting over the top of the ledge. Terra and Xehanort were trading blows, but it was clear that Terra was gaining the upper hand. Or so it seemed on the outside. But Vanitas knew Xehanort's true plan.

"Terra, stop fighting!" He shouted. He could feel Aqua's confusion inside them, but focused on exerting his will. He wanted to be in charge for this.

"Aqua?" Terra's focus broke; Xehanort got in a scarring hit with his goat-headed blade.

"Get away from him, we'll handle this!" Aqua added. Xehanort stopped fighting Terra to teleport close to them.

"Ah, so you chose the girl." Xehanort grinned eerily. Even though Vanitas had never mentioned his plan, he'd still managed to figure it out. That made his confidence waver; what else had the old man predicted?

"Ventus is dead then, I presume?"

"Yes," Aqua was the one to answer. So she'd caught on. Maybe she wasn't stupid after all. Terra choked in the distance, darkness radiating off of him.

"Excellent work, Vanitas," he offered the first line of praise Vanitas had ever heard from him. It was four years too late for that, though. "Now, deliver to your master the X-Blade!"

Vanitas's grip tightened on the weapon. Xehanort really thought that after all that work, all that pain, after letting his physical form be _destroyed_ – he really though that Vanitas would give up the result of his sacrifices?

"Yeah, about that." He grinned through Aqua's lips. "If you want it, you can have it."

Then he plunged the X-Blade through Xehanort's chest.

 **A/N: Thanks for being patient with this update! I can't promise I'll be more consistent in the future; I'm still working on a lot of WIPs at once, and I have a bad habit of not writing whatever I say I'm going to work on first. But regardless, this story is still being continued.**


	4. Save

**A/N: Uh, remember when I said this fic wouldn't contain KH3 spoilers? Yeah, about that...**

Light poured from the edges of where the X-Blade had impaled Xehanort. _Light._ After everything Xehanort had done, Vanitas had expected pure darkness to come rushing out.

He felt Aqua's horror at the sight, though he didn't know why. The old coot had nearly possessed one of her idiot friends, and nearly killed the other. He wished she would keep her stupid feelings to herself; he didn't want them ruining this moment.

"Any last words, Xehanort?" Vanitas pulled their lips into a smirk. He wasn't prepared for the old man's chuckle.

"You think this will stop me? Foolish boy. You have learned nothing." The light wafted up, encircling Xehanort's face, setting the gold of his eyes aflame. "I plan for _every_ contingency. Tell me, Vanitas, can you say the same?"

"I…" He took a step back. The X-Blade slid from Xehanort's chest, but the damage was done — he burst into a shower of lights, with only one larger orb left behind. Xehanort's heart.

 _He's still going to possess Terra,_ Vanitas realized. _I just did exactly what he wanted…_

" _No!"_ Aqua yelled within their heart before wrenching control of their body. She shot forward, chasing the glowing heart as it sped towards Terra's darkness-shrouded form. Though still in shock, Vanitas lent his strength to hers.

Terra engaged his armor as they bolted towards him — but he didn't need to. The X-Blade came arcing down inches from his face, slicing through Xehanort's heart. It dissolved like smoke and wisped away on the wind.

Less than a moment later, his barbed keyblade clanged to the hard earth. The aquamarine eye in its teeth started up at Vanitas, as if Xehanort was already watching him from beyond the grave. He kicked the keyblade off the edge of the cliff on reflex.

"He's gone. Even… even he couldn't come back from that," He whispered, if only to convince himself. His hands still shook; he gripped the X-Blade tighter to hide it. He just couldn't believe… after all this time he'd had to endure the old man's abuse… he was just _gone._ Just like that. He couldn't shake the feeling that he'd turn around and find Xehanort's keyblade back at his throat. Maybe he should've kept it in sight instead of knocking it off the cliff.

"Did we just… destroy a heart?" Aqua asked. He felt their throat close up with emotions that wouldn't leak out into Unversed. Why couldn't he get rid of them? Was Aqua holding them in?

"We better have," Vanitas answered, attempting to clear their throat. "It's what he would've done to us."

It was weird, talking to himself like that, but he didn't want to go back to the heart-pillar to talk to her. Especially not when Terra was still right next to them, backing away slowly.

"Aqua…?" He cautiously removed his helmet, revealing the shock plastered across his face. "What was… what did you do?"

"Terra… I…" Aqua started. Vanitas could feel the guilt and fear wafting from her half of their heart, as tangibly as if she'd created an Unversed. But they'd destroyed someone evil; shouldn't she and Terra be thrilled? That's what their Master had taught them to do, right? Whatever; he could twist this to his advantage.

"I killed him," Vanitas interjected in Aqua's voice. Her shock sent echoes through him. "Just like you killed the Master. Right, Terra? You have no right to judge me for this."

"What? I didn't— it wasn't like that," Terra defended, his grip tightening on his helmet.

"I didn't mean that!" Aqua said, taking control again. "Terra, I—"

"No, that's how you see it, don't you? I get it." He turned aside. "I can't be forgiven for what I've done. I know that, Aqua. I'll have to carry that with me forever."

"Terra…"

"But you saved me _and_ avenged the Master. You… did the right thing," Terra choked out. "Xehanort had to die."

"Then why are you upset?" Vanitas asked, partially to stall for time, partially because he was actually curious.

"Of course he's upset!" Aqua shouted. "I _murdered_ someone in front of him. _I'm_ upset! You're the only one who could watch that happen and feel nothing, you freak!"

Terra turned, staring at them with a concerned expression. Questions danced across his eyes. Vanitas was painfully aware of how his own golden irises would give him away, if Aqua's words hadn't already. But Terra didn't seem as ready as Ventus to jump to conclusions.

"...How did you get that weapon?" He finally asked.

Aqua winced. Tears pricked their eyes. Stupid, tears were useless; their emotions should be coming out as Unversed. His Unversed could handle Terra, keep him busy while they escaped. She couldn't let him know what she'd become, how badly she'd failed to protect them—

Wait. Those were _her_ thoughts. And he hadn't been trying to hear them.

As much as Vanitas wanted to slip back into the vision of their heart and figure out what was happening there, he couldn't take the time. He had to try his best to keep Terra from finding out what he'd done to Aqua, at least until they could get out of here.

"I beat Vanitas," he said, exerting all his power to remain in control of their body. "He and Ventus forged the X-Blade, but I beat him and took it. You looked like you could use the help up here."

Would Terra buy that? Vanitas could feel Aqua screaming inside them, trying to wrench control. But Vanitas had a better grip on how this worked; it was what he was created to do. What he was created to become. He could hold her off a little longer, so long as she didn't try anything crazy, like attacking his half of their heart again.

"Ven," Terra said, his eyes hardening. Apparently that was the last piece of evidence he needed. "Aqua always calls him Ven."

Vanitas cursed mentally. How could he miss such a stupid detail? He leapt back as Terra summoned his keyblade again.

"Tell me, what did you do to Aqua!"

"Terra!" She finally broke through his hold, reaching out their free hand. "Terra, it's Vanitas, he—!"

"Shut up!" Vanitas cut her off, yanking their hand back and clutching at their head. The armored gauntlet dug into their skin, but that wasn't nearly as painful as the war beneath. He couldn't keep this up forever, as much as she wanted to hide, she _needed_ to talk to Terra, needed to make him see she was still in here; light, if he tried to fight her, could she face him? She felt the strength coursing through her despite Vanitas's dark influence; with the X-Blade in hand, she might hurt Terra even if she tried not to—

"Get out of my head!" He shouted. Why couldn't he siphon her off the way he could with the Unversed? She was just one more negative emotion plaguing him, but his one and only coping mechanism was out of commission.

Terra wasn't waiting around for Vanitas to get ahold of himself. The taller keyblade wielder surged forward, bringing his long blade down with both hands.

For once, Aqua and Vanitas's halves agreed on a response. They raised the X-Blade to block the blow — and the resulting shockwave sent Terra flying back. He skidded across the plateau, nearly sliding off its edge.

That would've been too easy, though. He braced himself with Ends of the Earth and slowly rose to his feet. If Aqua hadn't been holding him back, Vanitas could've finished him off in that moment.

 _No, idiot, you can't destroy her friends. Not yet. You need some kind of collateral to keep her in line._

"I won't let you use my friends," Aqua hissed under her breath. Vanitas jumped, which must have looked stupid to Terra, who would just see Aqua muttering and startling herself. But Vanitas had to wonder — did that mean Aqua could feel his thoughts the same way he'd been sensing hers?

If so, his already tenuous backup plan just got a lot more complicated.

He didn't have time to think on that though, because Terra was rushing back in for another attack. All Aqua allowed him to do was block, though. Vanitas hissed. He held the most powerful weapon in existence, and all he could use it for was to _block!_

He couldn't complain too much though — even just blocking and parrying Terra's attacks wore the other keyblade wielder down. Each time their blades collided, Terra shook as if his whole body had been electrocuted. Meanwhile, Vanitas barely felt a thing.

"You can't win, idiot," he spat. "It's two against one."

"You're right," Terra said. "Me and Aqua against you."

Warmth spread from Aqua's half of their heart. The strange sensation was enough to momentarily freeze Vanitas, allowing her to take control.

" _What?"_ He gasped internally as Aqua forced their arm holding the X-Blade to drop – Just as Terra's Stun Edge struck their shoulder. They cried out, falling to one knee as the static paralyzed them.

"Aqua!" Terra knelt beside them, now glowing with his Critical Impact command style. Stupid. They still had the X-Blade; that one attack wouldn't take them down. But apparently he was as concerned about hurting her as she was about harming him. "I can't do this to you, not while you're still in there."

"Terra, you _have_ to," Aqua choked out, filling their eyes with water again. "You have to– put an end to–"

"I won't!" Terra shouted. "Aqua, I said I wouldn't do it to Ven, and I won't do that to you! We'll find a way, we'll…"

"You'll what?" Vanitas laughed through the tears that were dripping down their face. Salt water touched his tongue, making him wince. "You have no idea what you're dealing with. Aqua's heart is a part off mine now."

Terra searched their golden eyes, as if looking for any trace of his friend. Vanitas wondered if her light still shone through them.

"Aqua… if we fight, is there a chance it could save you?"

 _Save me? I came here to save him, and now I have more darkness inside me than he does…_ Aqua's thoughts trickled into Vanitas's mind. While he was thinking of a way to use that, she regained control.

"It's the only choice we have," she said. _And if it doesn't work – if you destroy me, at least I won't be able to hurt you or Ven. You'll be safe._

Now _that_ wasn't what Vanitas was counting on. He'd expected her to fight for her life, if only so she could keep protecting her friends. But if she saw herself as the bigger threat – if she was willing to sacrifice herself – then Vanitas was done for, too.

"Then I'll do it," Terra said, steeling himself. He meant it. He'd fight with everything he had, as if that had a hope of removing Vanitas's heart.

But it _did_ have a hope of destroying Aqua and himself both, if he couldn't wrench back control.

" _Aqua, don't do this!"_ He hissed inside their heart. _"Are they really worth it? Huh? Why should they get to live and not you!?"_

" _Because I'm already not living,"_ her reply came softly. " _You said it yourself. If our hearts are inseparable, then I'll never be whole again. I won't live like that."_

" _But– you idiot, we_ are _whole! That was the whole point of forging the X-Blade, we're_ one, _if you'd just stop fighting it and join with me–!"_

While he screamed inside, he also fought for control outside. But the X-Blade wouldn't move. His arm wouldn't move. Time seemed to slow down, and not from one of Aqua's spells this time. No, her will kept them held fast, forcing them to take the full brunt of Terra's Critical Impact command style.

Ends of the Earth dented the metal of Aqua's chest plate, caving it in painfully. The wind was crushed from their lungs. Vanitas gasped for breath, but couldn't get in enough air. Through it all though, he held tight to the X-Blade.

"You think…" He sucked in a hissing breath, "A few dents is... going to knock me out? Tch. You're even dumber… than you look."

While the blows had hurt in the moment, they had the side effect of allowing him to slip back into control again. This time, he wouldn't give it up so easily.

He stood, ripping off the dented metal breastplate. Beneath it his dark suit's veins now stretched across their chest. Terra gasped slightly as the sight, keyblade wavering.

"What's wrong, _Terra?_ " He pulled their lips into a mocking grin. "It's still me, isn't it? Your precious Aqua?Don't you still want to save me? _"_

"Nngh – don't talk to me with her voice!" Terra growled. Good, make him angry. He made his worst mistakes when rage took over.

Vanitas paced around him, always keeping the X-Blade between the two of them. He had to come up with something good, something to keep Terra from following when they left the Graveyard. Vanitas wasn't planning on sticking around here; he didn't need any stupid Kingdom Hearts. He already had the X-Blade. Xehanort's "new world" garbage could die with him.

"What? Are you afraid you won't be able to tell the difference between us?" Vanitas dropped the acidity from his voice, mimicking her usual tone so exactly that he almost scared himself. "I'm Aqua, and Aqua is me. Pretty soon there won't _be_ a difference."

"I won't let that happen!"

"Then you'll have to do a little better than just standing around shouting at us." Vanitas sneered. "Are you going to fight or not?"

Terra's breathing grew heavier; darkness wafted from his armor. His grip tightened on his keyblade. But still he held himself back.

"Heh. You're just as weak as she was."

That lit a fire in Terra's eyes. Finally he charged Vanitas again, slashing down with all his might.

" _Terra, no!"_ Aqua screamed inside. But Vanitas kept control.

He swung the X-Blade up, knocking Terra's weapon from his grip. It spun in the air before impaling itself teeth-first in the dirt.

"My turn."Vanitas grinned. Two crossed slashes of his powerful weapon sent Terra flying back, his armor scarred.

But Vanitas didn't stop there, in spite of Aqua's pleas. There was only way to keep Terra from coming after them. He had to be taught a lesson.

" _Vanitas, you can't do this! Please! I'll go with you, just – don't hurt him!"_

 _Oh._ He smiled. So her friends were still her weakness after all. He'd thought overhearing his thoughts might make her wise up, but even knowing his plan to use Terra as collateral, she'd still give herself up for him. Not that she'd had much of a choice – Vanitas might not want to _kill_ her friends, exactly, but he wasn't above a little bit of maiming.

"Really, now?" He asked as Terra's eyes widened. Disarmed, knocked flat, no chance that he could defend himself – and Aqua knew it. Meanwhile Vanitas was drawing power through the X-Blade, binding himself to it to keep her from breaking his focus.

" _Yes… really,"_ she whispered. He smiled.

"I can make that deal. But first things first."

He stabbed the X-Blade down into Terra's shoulder. His scream mingled with the sound of the weapon tearing through his metal armor. _Void, you'd think he's never been stabbed before._ The sound grated on Vanitas's ears, making him wince.

" _TERRA!"_ Aqua ripped through his hold, kneeling down at her friend's side. "Terra – oh light, I'm so– I'm so–"

Tears poured from their eyes like the blood from his arm. Still, they could see Terra staring up at them, blue eyes wide in shock… and in fear.

"Cur-curaga," Aqua's voice shook. The spell was strengthened by the X-Blade's power, but combined with her wavering voice, it averaged out to a regular Curaga's power. Some of Terra's flesh reknit, but not enough to completely stop the bleeding.

 _I… I did this… I was too late, and now Terra…_ Would he still be able to use his arm? Would he be able to fight again?

...Would he ever be able to forgive her?

" _I wouldn't bet on it,"_ Vanitas said while looking for cracks in her grip on their body. " _Like you said, you're darker than he is now. And even he didn't attack his own friends unprovoked. No matter what you do, he's going to look at you and see the face of a monster."_

"No… he… he won't believe that…"

"Gah…" Terra hissed and slapped his shoulder pauldron, disengaging his armor. "Aqua, if you're in there… go…"

"Go?" She echoed, tears still brimming in their eyes.

"I'll… find you. When I'm… stronger…"

"Right," she whispered, sniffing. "I'm so sorry, I didn't want–"

"Just go! While it's still you!" He exerted all his strength to say, fumbling in his pocket for a potion. She couldn't bear to watch him like that, so helpless – and she was completely unable to finish him off –

 _No!_ She tangled her fingers in her hair, trying to banish the thought. _Vanitas's_ though. He was leaking through again, already –

"Void, you're giving me a migraine," he muttered, shaking their head. It wasn't enough that he had to see through her eyes; he had to feel through her heart, too? That amount of hurt over her stupid friend was going to make him throw up. "But hey, if you want to get out of here, I'm all for it."

He held their hand out behind him, and a dark corridor spiraled out.

"Don't even think about following us," he hissed, "or that cut will be the least of your problems."

With Aqua still trying to call out to Terra, Vanitas backed them through the portal.

XXX

"So the old coot wasn't the one after all." Braig scratched at his eyepatch as he stared up at the unforgiving heart-shaped moon. "I'll give you props though, Xehanort, you've got guts. Picking me of all people for your little contingency plan!"

He laughed, fingering the now-pointed tips of his ears.

"That would've worked if I were just any old dude. 'Cept I'm not."

He picked up the large, wicked-looking keyblade that had fallen among the hundreds of the Graveyard's dead blades.

"Don't worry, though. You'll still get to see your Keyblade War through the one eye I've got left." He snorted. "Thanks for that, by the way. This vessel was one of my favorites. You have any idea how hard it is to aim with only one eye?"

He gave the keyblade a few swings. All these years, all these vessels, and it still felt the same in his palms as it had the day the Master first passed it down.

"Heh. Guess that won't be a problem anymore though. Thanks for the delivery."

If the piece of Xehanort's heart inside him could hear his snarky comments, it gave no reaction. But Braig knew enough to feel that the fragment was still there, despite what the girl had done to the old coot. The fragment didn't matter, though; he had plenty of practice dominating other people's hearts.

He held the keyblade up close to his good eye.

"I'm almost done here, Master. Took me long enough, but I think we've finally got someone who can get this Keyblade War moving."

She was gone, and she'd taken the X-Blade with her, but that didn't matter so much now. Kingdom Hearts was summoned, and until the X-Blade was destroyed, here it would remain. Keyblade wielders would gather here from all over the Worlds, ready to fight just like he'd seen happen millennia ago.

"Wonder if the kiddo remembers that yet," he said, remembering his fight with Ventus. He hadn't planned on getting involved past stalling Aqua, but when he'd seen what she was capable of – well, he had to keep the kiddo busy while she took on the old coot and then Terra. This was just too interesting to let it end yet.

Now, whether or not it would all be worth it… that all depended on what the girl chose to do. Which heart she decided to follow.

Either way, it was sure to be one hell of a show.

 **A/N: I had to edit this like 10 different times, but here we are! It turns out we're incorporating a little bit of KH3 stuff after all, mostly just the fact that Braig is Luxu. It's pretty late so I don't have a ton of other comments on this chapter, but things might get a little different from here on out. These first four chapters are all in the middle of action, but it might calm down a little bit now that there's no immediate threat – other than Vanitas and Aqua themselves, of course.**


	5. Plan

**A/N: Bet you thought you'd seen the last of me**

 **(Seriously though, if you're still reading this, thank you SO MUCH for your patience. I'm still working on the end of Stroke of Midnight, too, but this was easier to write currently.)**

Vanitas was drowning. This was wrong, wrong, _wrong,_ the darkness belonged to _him,_ but the dark corridor—it was fighting him, tearing through his heart— _their_ heart—flooding their lungs, and—

Aqua. It was all _her_ fault. Her pathetic light-filled body couldn't withstand the corridor, and—

 _And it's going to tear me apart, oh light, he's going to kill us but Terra's safe Ven's safe maybe I should just…_

 _Give in…_

"No!" Vanitas snarled against Aqua's fading thoughts. She was _drawing_ the darkness in, letting it lap up her light. They'd never be whole if she did that. In fact, they might not survive it at all.

The corridors wouldn't be satisfied with just a taste.

He gripped the X-Blade tighter, flashing between their heart and the dark corridor with every blink.

"I'm getting us out of here," he said through gritted teeth. Void, was this how darkness always felt to her? Nauseating and acidic—like venom seeping through his skin—and he'd thought her light was bad, burning like hellfire when they touched. Would _both_ hurt him now? Was there no escape?

 _Escape._ That was one thing he and Aqua could both agree on.

They brought the X-Blade down in unison, slicing through the dark corridor, through the fabric of space itself—

And stumbled out into a world Vanitas didn't recognize. Or… maybe he did? The earth was cracked, broken, fallen into the abyss and hanging in fragments from golden chains.

" _No,"_ Aqua gasped through their lips.

This was her home. Or what was left of it. Only the center of the Castle remained, silhouetted against the black sky like a crumbling tombstone.

Vanitas felt the tears rolling down their face even before Aqua's grief swept over him. The breath was crushed from their lungs. This—what _was_ this? Could she really hurt this badly over a crumbling castle? It had been so long since Vanitas had anything to lose… but Aqua was just beginning.

Her home… her friends… her Master, his keyblade the only evidence of his pathetic existence.

"Don't think about him like that!" Aqua's raw voice snapped. He still wasn't used to his own low tone underlying it, but he just snorted and replied in the same voice.

"If he wasn't pathetic, he wouldn't have lost to _Terra."_

Rage boiled inside him—no, inside _her,_ why couldn't she keep her stupid emotions to herself? Just because he was using her body didn't mean he wanted the baggage that came with it. That's what Unversed were for—getting rid of those useless feelings. But he couldn't do that anymore.

She shut their eyes, forcing them back into the vision of their heart. The whiplash of switching locations—switching _bodies—_ was still making him nauseous.

"Cut that out. Unless you want me throwing up on your heart."

"You're right. You're in _my_ heart," she hissed, tugging the X-Blade closer and making him stumble towards her.

His eyes widened at the coldness in hers. Had his darkness made some headway after all? Or had she lost her light to the corridors? Or—and this was a worrying possibility—had she not had enough in the first place? Was that why he was still stuck _stuck_ there was no escape why weren't they _whole_ there was light just past his fingertips but it just—wouldn't— _come—_

And this was why he needed the Unversed. All this stupid panicking would get him nowhere.

He swallowed, glad that his helmet still hid the emotions that surely played out on his face. ...Though that might be irrelevant if his thoughts overflowed into Aqua's half of their heart.

"Doesn't matter," he finally said. "Our hearts are inseparable. What's yours is mine."

"What's yours is _mine,"_ she corrected, leaning in so close that her breath fogged up his mask. The tearstained red around her eyes should have made her look weak, but instead just emphasized the pain she'd endured without breaking. "I know what you are, Vanitas. I know you're just an empty shell, a—a _parasite._ You will _never_ control me."

With that threat, she snapped their eyes open. Pulling hard enough to overcome his dizzy resistance, she knelt to pick up the discarded keyblade. What did she plan to do with that weak thing? They had the _X-Blade._

(But the X-Blade required them _both,_ all that power and he couldn't _use it,_ and it wasn't like he needed Kingdom Hearts, he just wanted a body with _light_ and he wanted it to be _his,_ but Aqua was so stupidly _stubborn—)_

She groaned and brought her knuckles to the bridge of her nose, recklessly swinging the X-Blade with the action. An arc of light went slicing off into the darkness.

"Huh," Vanitas deadpanned through their mouth. "That's not bad."

"Not—? We shouldn't even have this power! Now stop—stop thinking so loud so I can concentrate!"

"Stop thinking? Who do you think I am, Terra?"

She just growled and tried to point the X-Blade at him—but considering they were sharing a body and currently looking out on the real world, there was nowhere to turn. She just ended up firing a ray of light off into the already-scarred side of the castle.

 _Doesn't matter. I can still stop him,_ she thought, clear enough for him to hear.

"Stop me?" He blurted, torn between wanting to laugh and suppressing a shudder of fear. Did she know something he didn't? He doubted it, but… she _was_ stalking them towards the ruins of the castle with a lot of determination for someone with no plan.

"You'll see soon enough."

Her thoughts were otherwise shielded from him—no, not _shielded,_ but overpowered by the all-consuming hate she directed his way. It boiled like a fever under his skin, forcing him to his knees in their heart. She just wanted him _out,_ she didn't care how much it hurt; she wasn't darkness she _wasn't_ she _wouldn't give in_ even though she hated him _so so much—_

He gasped for air that he shouldn't even need. He hadn't known it was _possible_ for her to hate so deeply. The only person he hated like that was… Xehanort, probably. Maybe Ventus, but that was more complicated. Too many Unversed mixed together, and without the ability to release them, Vanitas couldn't puzzle out the exact emotion.

Aqua paused, their foot hovering at the top of the crumbling steps. "You don't… hate me?"

Oh. So she'd heard that, then. Inexplicably, his own embarrassment pushed back the tide of her resentment. At least he could breathe again.

He should hate her on principle. She was everything he wasn't, and she had everything he didn't.

Or… she had. Until he'd taken it away.

Where was the satisfaction he'd expected from that? Probably still buried under Aqua's own fury.

"You don't even care," she realized. "You _don't_ hate me. Light, you really are empty."

She stalked off again, shoving through the heavy castle doors before Vanitas could articulate his shock.

He _wasn't_ empty. He was literally formed of negative emotions that he could bend to his will. No matter what his name said, no matter what Aqua said—he wasn't _nothing._

He had his darkness. He had her light. He _wasn't empty._

Her thoughts bled to Terra as she guided them through the castle. He would've stopped her, but what was the point? They couldn't just stand in the courtyard forever, and it wasn't like he had any better place to go. At least this way he might learn something of Aqua's weakness, something he could use…

 _For what? We're one person. I can't destroy her._

At least she wasn't listening to his thoughts now, too busy mourning the pain she'd caused her friend. He caught flashes of memory… a promise she'd made her Master, it sounded like, though he couldn't quite piece the fragments together. Protecting Terra, not letting the darkness hurt him, blah blah blah. Nothing useful.

Nothing, until Aqua turned her Master's old keyblade towards the backside of the middle chair in the great hall.

" _What are you doing?"_ He tried to demand, but his voice didn't reach her lips. While he was sure his hand still clenched the X-Blade in their heart, it had no effect on what she chose to do with the other key.

And she chose to… lock a giant chair, apparently.

 _Where is all that wind coming from?_ Yes, there was a glowing magical lock on the back of the throne, but somehow that detail was less surprising.

He needed to focus—whatever Aqua was doing, it couldn't be good. Not good for him, anyway.

"Let… go!" She protested as he tried to pull their arm back to their side. The X-Blade already dangled uselessly, but the Master's blade glowed with warm, heavenly, _painful_ light.

It was enough to push Vanitas deeper into their heart, just for a moment. But that was long enough for Aqua to turn the key, and for the transformation to complete.

 _White,_ was all he could think when they blinked their eyes open. White, blinding _white._ No more signs of debris or decay. Whatever she'd done to the place, it had restored the castle's structure, if given it a terrible interior design. Was that really what she'd been so determined about? It wasn't like blinding walls were going to force him out of their heart.

"They aren't meant to," Aqua finally said, their voice quieter than he expected. "All who visit this land will be lost to oblivion…"

"What?"

"I can only hope, now that I'm not… me… that will include us."

"What are you _talking_ about?"

He wanted to look her in the eyes as he demanded answers. But they were still stuck staring at the mesmerizing _pulse, pulse, pulse_ of one glowing chain as it ran up the white wall.

"Castle Oblivion. Here, no one will be able to find us… and we won't hurt anyone else."

Their gaze dropped to the X-Blade as she said it. The Master's old blade vanished from her other hand in a shower of sparks, but try as she might, the greater weapon couldn't be banished so easily.

Vanitas could hardly believe she wanted to _try._ They had so much power; wasn't there anything she wanted to do with it? Anyone she wanted to hurt?

"Only you," she said, sounding more tired than bitter. Had he finally worn her through the stages from denial to acceptance? "You haven't tried to do much, either. What was your plan? Possess me, and…?"

Embarrassment returned in full face-flushing force. He'd never really gotten that far. Forge the X-Blade, become whole, start the Keyblade War… and that last one had just been for Xehanort's benefit, really. It didn't matter now that the old geezer was dead.

"Of course." She sighed. "You really expect me to believe that?"

"I can't lie in my own head, you know," he spat back, running his thumb back and forth across the X-Blade's handle. This conversation would've felt better inside their heart, but Aqua was stubbornly keeping their eyes open. Maybe it was because she wouldn't be able to see his expressions through his mask even if they faced each other. "Believe what you want. I still won."

"Won _what?_ We're both prisoners here."

They slumped to the ground, resting against the back of the giant throne. The X-Blade clattered hollowly against the floor, slipping just out of reach of their fingertips. Panic flashed through him, but nothing happened. He was still just as present in Aqua's body as before. Apparently only the internal X-Blade mediated their shared consciousness.

"Our heart wouldn't be a prison if you would just _join with me,"_ Vanitas insisted.

Aqua scoffed. "Even if I wanted to, how do you suppose I would do that?"

They blinked as Vanitas's shock washed over them.

"I… I don't know."

He didn't know.

He was stuck in Aqua's body. No way out. No plan.

Infinite power, no ability to use it… without working together with _her._ The girl who hated him enough that it caused him physical pain.

Aqua's strangled laugh dissolved to tears as they curled up on the cold floor.

And maybe, just maybe, a few of those tears were his own.

XXX

"I see." Yen Sid stroked his beard, but remained seated behind his desk, as if Ven and Terra _hadn't_ just told him that the universe was ending.

The universe was ending. Wasn't it? The heart-shaped moon had still been hanging low above them when Terra and Ven fled the Keyblade Graveyard. Ven hadn't known what it was, what it meant—but the bone-chilling terror that gripped him had felt _familiar._

Familiar, and definitely warranting the old not-Master _standing up,_ at least.

"We need to save Aqua," Terra repeated, as he had at least four times during their story. Ven agreed, of course—seeing Vanitas's eyes in Aqua's face had been _terrifying._

That could've been him. Vanitas had wanted _him_ to forge the X-Blade. Aqua had sacrificed herself to save him. If he hadn't been stupid, if he hadn't been frozen by Xehanort…

He shivered under the blanket Terra had found for him and let his friend finish doing the talking.

"Is there any way we can separate her heart from Vanitas's?" Terra asked. "If we split them, the X-Blade will go away, won't it?"

Yen Sid sighed and shook his head. "It is not that simple. Separating two hearts once unified…" His eyes flickered to Ven, "that would cost a price I do not believe you could pay."

"What, like… she might… die?" Ven whispered from where he sat on the ground. They'd gone through too much today to be shy about saying it. "But Vanitas and I were the same person once. And we both survived."

"How that happened remains a mystery. There are other forces at work, I sense."

Yen Sid stared out the window, to where the stars flickered fitfully. Worlds, with their hearts calling out to the great Kingdom Hearts, the retired Master had explained. His own Tower was between worlds, lacking a true heart of its own, which somehow kept it stable. Ven didn't understand all the details.

All he knew was that Kingdom Hearts would stay hanging in the Keyblade Graveyard sky until the X-Blade was destroyed.

And for the X-Blade to be destroyed…

"We have to risk it," Terra said, fist clenching. "There has to be a way. Aqua's our best friend. We can't let Vanitas keep her."

His shoulder pauldron still bore a deep gash that Terra wouldn't acknowledge. And Ven wouldn't ask. But every time Terra spoke of Vanitas, his fingers drifted towards the marred metal.

"Terra. I do not want to give you false hope." Yen Sid leaned forward, his fingers steepling over his desk. "There is a fair chance that _nothing_ will be able to save your friend. The more time that passes, the deeper their union will grow."

Terra's growl took Ven by surprise.

"Then tell me what I need to do already! I don't care what the cost is, I'm willing to pay it!"

Their stares met in a silent battle, one that had Ven shirking back. But Terra was right. It was Ven's fault Aqua was like this; he would do _anything_ to save her.

"Tell me, Terra. Would you be willing to steal a Princess's heart?"

He stepped back, gaping for a moment before his jaw snapped shut. His brow furrowed as he met Ven's eyes.

"I…" Terra floundered before shaking his head. "Is that the only way?"

Yen Sid lifted his hand, and a thick book came floating from the shelf towards him. "The legends are incomplete, but Xehanort dedicated his younger years to compiling them. This is all I have of his studies."

That was _Xehanort's_ book? Ven's eyes widened, but Terra quickly took it.

"Does it say what we need to do?"

Yen Sid sighed. "It details the creation of a Keyblade of People's Hearts. This particular keyblade was intended to unlock the darkness within a person's heart… but under these circumstances, it may separate a heart of darkness from a heart of light. However, nothing is set in stone. Such experiments have not been attempted in centuries. Nor should they have been."

Again, his heavy gaze fell upon Ven. It wasn't like he'd _meant_ to get torn in two, but the way Yen Sid looked at him…

He looked away to where Terra was flipping through the tome, his eyes widening with each new page.

"This is…" he swallowed. "Will this really work? If we… if we use the Princesses' hearts…"

Ven flinched at the idea. He'd said _anything,_ hadn't he? But this… this was wrong. They couldn't just decide that Aqua deserved her life more than whoever the Princesses were.

"These are only theories. There is no way of knowing for certain. You see why I hesitate to suggest this course of action."

But he _had_ suggested it. Maybe Yen Sid did realize this was more serious than he let on. But then why wouldn't _he_ do something about it? Was he stuck in this tower?

"It's all we've got." Terra grit his teeth and snapped the tome shut. "We have to try. Come on, Ven."

"Wait, Terra—!"

But he was already out the door.

"Ventus," Yen Sid said before Ven could drop the blanket and follow.

"What?" He snapped. He didn't have time for this; what if Terra left without him? And what if Terra _actually stole another heart?_

"This _is_ the only way. If you cannot free her… it will be up to you to destroy the X-Blade through whatever means necessary."

"Me? But—but you're a Master! Why can't _you_ do it?"

" _Former_ Master," he corrected, though his face finally showed a trace of regret. "My magic has come with great costs. Not to the same extent as Xehanort's fall into darkness, but costs all the same. Should you fail, I will use the powers I still possess to delay the coming Keyblade War."

"Keyblade… War?" That same familiar terror clawed at his throat, though he was pretty sure the Master had never taught him anything about a Keyblade War.

Yen Sid smiled grimly. "I hope it will not come to that."

When the former Master provided no other explanation—and Ven realized he didn't have time to wait for one—he rushed off down the stairs.

"Terra!" He called, hoping he wasn't too late. But he wasn't; his friend's back was framed by the doorway, silhouetted in front of the mystical twilight sky.

He panted, hands on his knees, before speaking.

"You're… you're not really going to do this, are you?"

Terra glanced over his shoulder. His face was set like stone in the brief moment before he activated his armor. When the light flashed over him, he was left in battered gold and copper metal. Wasn't that supposed to repair itself when summoned back? If it was still broken, then—it must have been the X-Blade that did this to him. It was even more powerful than Ven realized.

Maybe it could even break keyblades themselves.

They _had_ to stop Vanitas from using it—but could they really do it like this?

"It's the only way, Ven." Terra's voice echoed eerily out of his helmet. "I promised you. The three of us can never be torn apart."

 _Put an end to me,_ Ven had asked him. Terra had denied him then. If it came down to it… would Aqua want the same thing?

If she asked them to… could Ven put an end to _her?_

"I'm coming with you." Ven's voice left no room for argument. He didn't know if they could really use the Princesses' hearts—he didn't _want_ to—but he couldn't let Terra try alone.

And… it was his fault Aqua was like this, after all.

Did he have any right to object to Terra's plan?

"...Alright," Terra relented. Probably because there was no where else for Ven to go. It had come out during the trip to the Mysterious Tower that their Master had been… struck down. But Ven didn't have time to process that now.

He couldn't save Master Eraqus. But Aqua was still out there.

So Ven summoned his glider, and followed Terra into the stars.

 **A/N: Thanks to kingdomheartssynctophiliac on tumblr for double checking that Ven doesn't know who the Princesses of Heart are. He's met them, but he doesn't know that they're Princesses specifically.**

 **Anyway, finally getting some plot set up! Sorry that meant a lot of info dumping in that last section.**

 **Probably no more updates until after the DLC is released because I NEED that Luxu info. He will likely be making a return next chapter**


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